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arXiv 2103.09838astro-ph.GA
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Milky Way盘中的恒星迁移和化学富集:一个混合模型

Stellar Migration and Chemical Enrichment in the Milky Way Disc: A Hybrid Model

James W. Johnson, David H. Weinberg, Fiorenzo Vincenzo, Jonathan C. Bird, Sarah R. Loebman, Alyson M. Brooks, Thomas R. Quinn, Charlotte R. Christensen, Emily J. Griffith

摘要:

我们开发了一个银河系化学演化的混合模型,该模型将化学富集的多环计算与恒星迁移的处方以及由宇宙学流体动力盘星系模拟提供的恒星星族垂直分布相结合。我们的基准模型采用经验激励形式的恒星形成规律和恒星形成的历史,与流出的质量负载的梯度调整,以重现所观察到的金属丰度梯度。通过这种方法,该模型再现了银河系盘丰度结构的许多引人注目的定性特征:(i)[O/Fe]-[Fe/H]分布对半径$R_\text{gal}$和中面距离$|z|$的依赖性,(ii)[O/H]和[Fe/H]分布随$R_\text{gal}$和$|z|$的形状变化;(iii)太阳下金属丰度[O/Fe]分布较宽,[O/Fe]分布随$R_\text{gal}$、$|z|$和[Fe/H]的变化而变化;(iv)[O/Fe]与恒星年龄之间存在紧密的相关性,[O/Fe] $>$为0.1;(v)由Ia型超新星速率的迁移引起的变化引起的年轻和中年$α$增强型恒星的种群;(vi)非单调的年龄-[O/H]和年龄-[Fe/H]关系,具有大的分散性,太阳金属丰度附近的中位年龄为$\sim$ 4 Gyr。具有增强的恒星形成率$\sim$ 2 Gyr ago的观测动机模型改善了与观测年龄-[Fe/H]和年龄-[O/H]关系的一致性,但恶化了与观测年龄-[O/Fe]关系的一致性。我们的模型都没有预测[O/Fe]分布与观察中看到的独特的双峰,这表明需要更戏剧性的进化途径。用于我们模型的所有代码和表格都可以通过化学进化通用积分器(VICE; https://pypi.org/project/vice)公开获得。

英文摘要:

We develop a hybrid model of galactic chemical evolution that combines a multi-ring computation of chemical enrichment with a prescription for stellar migration and the vertical distribution of stellar populations informed by a cosmological hydrodynamic disc galaxy simulation. Our fiducial model adopts empirically motivated forms of the star formation law and star formation history, with a gradient in outflow mass loading tuned to reproduce the observed metallicity gradient. With this approach, the model reproduces many of the striking qualitative features of the Milky Way disc's abundance structure: (i) the dependence of the [O/Fe]-[Fe/H] distribution on radius $R_\text{gal}$ and midplane distance $|z|$; (ii) the changing shapes of the [O/H] and [Fe/H] distributions with $R_\text{gal}$ and $|z|$; (iii) a broad distribution of [O/Fe] at sub-solar metallicity and changes in the [O/Fe] distribution with $R_\text{gal}$, $|z|$, and [Fe/H]; (iv) a tight correlation between [O/Fe] and stellar age for [O/Fe] $>$ 0.1; (v) a population of young and intermediate-age $α$-enhanced stars caused by migration-induced variability in the Type Ia supernova rate; (vi) non-monotonic age-[O/H] and age-[Fe/H] relations, with large scatter and a median age of $\sim$4 Gyr near solar metallicity. Observationally motivated models with an enhanced star formation rate $\sim$2 Gyr ago improve agreement with the observed age-[Fe/H] and age-[O/H] relations, but worsen agreement with the observed age-[O/Fe] relation. None of our models predict an [O/Fe] distribution with the distinct bimodality seen in the observations, suggesting that more dramatic evolutionary pathways are required. All code and tables used for our models are publicly available through the Versatile Integrator for Chemical Evolution (VICE; https://pypi.org/project/vice).

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